Cylinder Head Rebuilding & Valve Train Flashcards

What is the purpose of measuring valve stem runout (stem straightness) before reusing a valve?

Answer: A bent stem causes guide wear, side loading on the seat, and erratic valve sealing

A bent valve stem causes the valve to wobble in the guide, accelerating guide wear, creating an off-center seat contact, and producing inconsistent sealing.

On a hydraulic roller lifter engine, what is the specified preload range typically applied to the lifter after zero lash is established?

Answer: 1/4 to 3/4 turn past zero lash

Hydraulic lifters require 1/4 to 3/4 turn past zero lash to keep the plunger in its operating range; too little causes noise and too much holds valves open.

Which type of valve spring design is most resistant to harmonic surge at high engine speeds?

Answer: Variable-pitch (beehive or dual) spring

Variable-pitch and beehive springs have progressively changing coil spacing, which shifts the resonant frequency away from the engine's operating RPM range and suppresses harmonic surge.

What condition does a valve spring tester measure, and at what point is a spring considered unserviceable?

Answer: It measures spring pressure at a specified compressed height; a spring is unserviceable if pressure is more than 10% below spec

Spring testers compress the spring to the installed height and measure the load; a reading more than 10% below spec means the spring has weakened enough to allow float at high RPM.

When installing valve keepers (locks) in a cylinder head, what tool-related practice prevents them from unseating during assembly?

Answer: Apply a small amount of assembly grease to the keeper grooves to hold them in place while the spring compressor is released

Assembly grease holds the keepers in the groove while the spring compressor is slowly released, preventing them from popping out and becoming a safety hazard or damaging the engine.

An engine is found to have excessive valve guide clearance. Which repair method restores OEM-equivalent performance while also allowing for future service?

Answer: Install a thin-wall bronze guide liner (Knurling is only a temporary fix)

Thin-wall bronze guide liners are pressed into the bored-out original guide, restoring the bore to OEM diameter with excellent wear resistance and the ability to re-ream the liner in future service.

What is the purpose of the valve rotator (Roto-cap) fitted to some exhaust valves?

Answer: To slowly rotate the valve each time it opens, distributing wear and preventing carbon buildup on the seat

Valve rotators cause the valve to turn slightly with each open/close cycle, preventing carbon deposits from building up on the seat and distributing thermal and mechanical wear evenly around the valve face.